"Apple has changed its iOS developer guidelines, adding a clause (on September 12, a source tells me) that reads: 'Apps that display Apps other than your own for purchase or promotion in a manner similar to or confusing with the App Store will be rejected.' That's a change that could have wide-reaching effects, especially on promotion models that offer developers a paid top slot on app recommendation offerings like FreeAppADay, Daily App Dream and more." Weird clause. Doesn't really seem to address any issue I can think of.

I've been seeing a lot of Android apps that bring up a dialog box advertising other apps from the same author/publisher on every start recently. Apple may be trying to head that kind of shit off at the pass.
Edit: looking at the wording, it isn't clear if that kind of ad would be caught by the new clause, so yeah, probably just trying to make sure they remain in control of the ecosystem and prevent sub-vendors from getting a slice of the pie.